Formula to Update Field based on another field being changed

[khopper]

I need to update a field based on another field being changed.
Example: If I update Opportunities-> Field "Stage" - doesn't matter what I choose it can be anything as long as it was changed.
I want to update another field called "Stagedt" with the current date and time that the field "Stagedt" was changed.

I found this but it I don't want to update that field if anything in the Opportunity was changed only a specific field was.
entity\isAttributeChanged(ATTRIBUTE)
would something like "entity\isAttributeChanged.fieldname(ATTRIBUTE )" work?

[khopper]

I made a workflow rule for this but and it works but if i have to add any options to it I will have to remember to add it to the workflow rule.
I just wanted it to update that field no matter what has been chosen. The workflow rule is limited to the ANY which I have to make sure I have them ALL listed in it.

[tanya]

Hello
About formula:
ifThenElse(entity\isAttributeChanged('stage'), stagedt = datetime\now());

About workflow:
you can add several workflows for the one entity types, with different conditions and actions